Human papillomaviruses (HPVs) are causative agents in ano-genital carcinomas in normal hosts (anal, vulvar, cervical and penile carcinomas), and cutaneous squamous cell carcinomas in immuno-suppressed individuals and in individuals with epidermodysplasia verruciformis. The interaction of HPV oncogenes with cell cycle regulatory proteins, particularly p53 and the retinoblastoma protein, is critical for their immortalization properties and the progression of HPV induced lesions to carcinomas. The HPV E6 gene from cancer-associated HPV types (such as HPV-16) binds to p53 and a ubiquitin ligase protein E6-AP. The formation of a complex between E6-AP, p53, and E6 leads to the ubiquitin dependent degradation of p53, and thereby to loss of p53 dependent apoptosis and cell cycle regulatory functions. Papillomavirus types from non-cancer associated HPV and animal papillomaviruses also can bind E6-AP, but they do not associate with or target the degradation of p53. In order to understand the interactions between E6, E6-AP and their cellular targets, this application proposes to analyze the interaction of HPV16 E6 with E6-AP and their cellular targets, this application proposes to analyze the interaction of HPV16E6 with E6-AP and p53 in yeast. We will isolate point mutants of HPV-16 that interact with E6-AP but fail to interact with p53 in order to map those features of papillomavirus E6 genes that are critical in the targeting of cell cycle regulatory proteins for ubiquitin mediated degradation.